Confused by black layer around GND pad

I am working with an SMT part that has a large GND pad in the middle. It requires this ground pad to be soldered to a larger copper pour region for heat spreading purposes.

I designed the footprint in the footprint editor and placed it on my PCB. Then I drew the required copper pour region around the GND pad. What I see in the PCB editor is this:

I am confused by the black region surrounding the ground pad (indicated by the green arrow, which was drawn by me, not Kicad). Is this a region of solder mask surrounding the pad? It does not disappear when I hide the F.Mask layer, so I’m not sure what it is.

Thank you.

As a new user, I wasn’t able to include a second image in my first post. But I want to add this to the question.

The display in PCB Editor gets even weirder when I switch the copper pour fill from “Solid Fill” to “Hatch Pattern.” In Hatch Pattern, a bunch of black boxes appear inside the copper pour zone:

What are those 21 black polygons that have appeared within the dark red F.Cu fill zone? Again, they do not disappear when I hide F.Mask.

The black stuff is “nothing” / “void” / “Background”.

You may as well be watching next to your PCB.

The thin black line around the pad is called a “thermal relief”. It is an interruption of the copper, and it’s use is to make it easier to solder the pad to the GND plane.

Thermal via’s are a part of the zone properties:

If you want to use the copper zone as a heat sink, then you have to turn off the thermal vias. By default this is done with the copper zone, but you can override this by setting it for a footprint, or for a single pad.

The hatch pattern, is a hatch pattern. A solid fill usually is better. Hatch patterns are a bit out of fashion these days. In the old days there were problems with making PCB’s flat if there was a great imbalance in the amount of copper between the top and bottom layer. The hatch patterns were invented back then to still have a reasonable GND (or power) plane, while still having approximately the same amount of copper on both the front and back layers, and thus to reduce warping during production.

Thermal via → Thermal relief. Blame it on the keyboard, It was not me, the buttons moved.

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If you want the zone to have thermal reliefs by default, but want a distinct pad without, change the pad properties:

Thanks for the reply. Everything you’re saying makes sense.

(“Thermal via” means something different to me. Thermal vias, in my world, refer to small holes you drill to connect from the front copper and the back copper layers to spread the heat from the IC package to more copper surface area. I actually do plan to add about 35 thermal vias inside that big GND pad, but I haven’t gotten around to that yet.)

Since I do want to use the pad as a heat sink, should I turn off “Thermal relief” entirely as suggested in your image?

The thermal reliefs are the breaks in the pad boundary, right? The blue arrows below:

I just want to confirm we’re talking about the same thing when using the term “thermal relief.” Thanks.

The blue arrows show what is called the thermal relief spokes, the black area is the thermal relief gap. Both of them consitute the thermal relief.


Thank you @straubm. That makes sense.

Btw, with the “spoke angle” setting you can do things like so (set to 45°):


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Is there a benefit to the 45 degree angle, @straubm?

The image you show looks hard to solder because paste applied to the 2-GND pad is going to spill out those big thermal relief spokes during reflow, no?

It’s normal that solder paste distributes a bit around a pad and the connection of a footprint. It’s also a combination with the solder mask layer that prevents the solder from spreading too far, and the solder stencil aperture (and thickness) that defines how much paste is deposited in the first place. Those things have to be balanced.

45 degree angle usually does not matter much. Sometimes there is an unfortunate interference with other things around the pad, and rotating the spokes can then be used to improve the connection.

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It doesn’t take much to promote yourself, see here.

Left click your ID then left click the new larger version and go to summary to see what you still need to do.

The image was certainly ‘just to show possible effect’.

Changing the relief spokes angle will change noting to it what you are speaking about.
Past will not spill out as thermal relief spokes are covered by solder mask.

I’m sure that was a slip of the tongue.

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When clicking at my ID at top of the message second left click does nothing for me :frowning:
When clicking at my ID at top of the screen second left click hides what was opened by first one.

(and 20 chars)

Sorry @Piotr, I should have written:
Left click your ID then left click the new larger ID that shows.

I landed in information about me with Activity tab opened.
I don’t see there any information about what to do to promote myself.
Do the new users have there some description of what they have to do to promote themselves?

The link I placed in my reply shows what is required by Rust to be come “Basic” . Clicking on his ID shows his activity, so he can see what he needs to do to promote himself to Basic.

Rust needs to read 19 more posts and open 4 more topics to become Basic.

Piotr cannot be promoted, he has reached the top of the heap already! :grin:

The link I placed in my reply to Rust is here. It is a link to the FAQ for new members. It is often easier for new members to promote themselves than wait for Admin to arrive.

According to what I have tested till now.
When I open with that method my information I land with Activity tab active and don’t see the needed information.
When I open someone else information I land with Summary tab open and see what is needed to compare with data from FAQ.
It was clear (from the beginning) that FAQ tells what are the tasks to be done (I know that FAQ exists), but as I have previously tested what you said only at my ID (so not seeing a Summary) it was not clear for me that you only write about two left clicks and nothing about that then you should select Summary.
May be you just didn’t noticed that if the user clicks his own ID he don’t see Summary at once or may be it works differently for you and me. May be something else (Cookies) decide with what tab the personal information page is opened.

You are correct. I have altered my comment to Rust.
I will remember that in the future when replying. Thankyou.